Always make sure to use microwave splatter protectors to keep your microwave clean and avoid causing smells to persist way after use. To clean your microwave, you can handwash the plate and rollers in the sink and towel dry because you will need these when you go to boil a cup of water for 2-3 minutes. When you do this, the steam actually helps soften the build making it a breeze to clean. WARNING, the cup of water will be extremely hot. Please proceed with caution and work around the cup. Allow the cup to cool for about ten minutes and then remove.
Change your exhaust filters if you have an over the range microwave. If you cook a lot everyday, the grease that builds up in the exhaust filters can cause them to clog. Change these about every 6 months just depending on how much you cook. I like to keep a spare set to allow me to clean the dirty set. Some units also contain carbon filters. These carbon filters cannot be cleaned and must be replaced.